Technical Field
The present invention relates to semiconductor processing, and more particularly to devices and methods that employ extremely thin semiconductor-on-insulator (ETSOI) substrates with active regions that are doped without needing to recrystallize the active regions.
Description of the Related Art
Metal oxide semiconductor field effect transistors (MOSFETs) often suffer from performance loss due to carrier leakage. One of the major leakage sources of MOSFET devices is drain-to-substrate leakage. Here, charge from the drain leaks into the substrate. This is made even more severe when epitaxially grown layer (epilayers) have defects. One method for addressing leakage into the substrate of the device is to provide a buried oxide layer. In a silicon-on-insulator (SOI) structure, a buried oxide layer is disposed between a base (bulk) substrate and a thin silicon layer. The devices are formed in the thin silicon layer, which is isolated from the base substrate by the buried oxide layer.
An extremely thin SOI (ETSOI) can reduce drain-to-substrate leakage and provide high field effect mobility. However, it is difficult to form source and drain regions using implantation methods since such methods damage the extremely thin layer during the implantation. In addition, the ETSOI is so thin that once the source and drain regions formed in the thin material are amorphized after implantation, the source and drain regions cannot be recrystallized since there is no seed layer below them to recrystallize them. Therefore, a recrystallization anneal has limited or no effect on reordering the crystalline structure of the source and drain regions.